So initially I decided to be clever and track needs-attention without
iterating through pages. Bad idea - this works fine as soon as there are no
notify emissions. Unfortunately that can still happen, and does happen in
inspector. Oh well, O(n) it is.

Chun-wei Fan authored Jan 21, 2023 and Alexander Mikhaylenko committed Jan 21, 2023

Returning a value in a function that has a void-rettype triggers a C4098
warning on Visual Studio, which is considered an error in glib-2.68.x or
later. Fix that.

We depend on new GLib now, so the real macros are always available.